Animals are multi-cellular, eukaryotic heterotrophs


  • Must ingest organic materials
    • consume, breakdown internally with enzymes


  • Lack structural support from cell walls
    • extracellular proteins connect and strengthen cells
    • most abundant are collagen (not found in plants/fungi)


  • Cells organized into tissues for “True Animals”
    • similar cells acting as a functional unit
    • muscle & nervous tissue allows animals to move


  • Body plan = programmed development driven by evolution

Body plans are coordinated to optimize biological function

Hox genes are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals

Embryonic development key for animal diversity

  • Fertilized zygote undergoes cleavage
    • mitotic cell divisions without cell growth
    • rapid division but overall size stays same
    • protostome vs deuterostome = alignment of these cells


  • Early multicellular stage called a blastula (hollow ball)


  • Germ (tissue) layers develop in next stage (gastrulation)
    • eventually develop into body parts


  • Many animals have a larval and adult stage
    • larva are sexually immature
    • larva look, live and eat differently

Devlopment of the blastopore in different animal groups




  • Blastopore: opening of central cavity of an embryo


  • In most animals a second opening forms at opposite end
    • become openings of digestive tube


  • Diploblasts: opening to gastrovascular cavity
  • Protostomes: blastopore becomes mouth
  • Deuterostomes: blastopore becomes anus

Germ layers (primary cell layers in development)



  • Sponges (0), Diploblasts (2), Triploblasts (3)
    • germ layers develop into tissues and organs


  • Ectoderm:


  • Endoderm:


  • Mesoderm:

Body Cavities in Triploblasts



  • Fluid/air spaces form within mesoderm layers
    • digestive track and body wall


  • Body cavity called coelom
    • cushions organs
    • fluid resistance for muscles
    • allows organs to move independently


  • Not all triploblasts have a coelom

Mammals develop subdivided body cavities from coelom


  • DONT memorize!!


  • The dorsal cavity and the ventral cavity are the largest body compartments.


  • Dorsal body cavity includes the cranial cavity, enclosed by the skull, and the spinal cavity, enclosed by the spine


  • Ventral body cavity subdivided into 2 compartments
    • thoracic contains the lungs and heart
    • abdominopelvic contains the kidneys, ureters, stomach, intestines, liver, gallbladder, pancreas, bladder, anus and reproductive system

Evolution of animal size and shape



  • Animal body plans are expressions of the genome, but the product of millions of years of evolution


  • Animals body plans are constrained by physical laws
    • diffusion, size and movement, heat exchange
    • gravity (land), pressure (aquatic)


  • Example: Properties of water and animal shape
    • water more dense than air = surface bumps cause drag
    • natural selection favored tapered smooth bodies
    • convergent selection across aquatic vertebrates

Form and function in biology

Example: Diversity of bird form is tremendous

Movie monsters are mostly not possible…. Godzilla

  • At that size, Godzilla’s heart wouldn’t be able to pump blood to the brain.


  • Brain would send messages too slowly to muscles, so wouldn’t be able to move properly


  • Godzilla would have to sunbath constantly to stay warm

Exchange with environment limits animal bodies


  • Basic Animal Function: uptake nutrients, expel waste and exchange gases
    • occurs across plasma membrane of all cells


  • Simple internal body plan: Cnidarians (jellyfish)
    • outer tissues exposed to environment
    • gastrovascular cavity also open to environment

Exchange with environment limits animal bodies


  • Basic Animal Function: uptake nutrients, expel waste and exchange gases
    • occurs across plasma membrane of all cells


  • Body plan optimized for surface area: Flatworms
    • thin, flat shape
    • lots of outer cells exposed to environment

Exchange with environment limits animal bodies


  • Basic Animal Function: uptake nutrients, expel waste and exchange gases
    • occurs across plasma membrane of all cells


  • Many animals (like humans) have more complex internal bodies
    • reduces total # of cells on outer surface
    • volume > surface area
    • ‘think’ whale versus flatworm


  • Internal structures for exchange evolved…
    • highly branched or folded
    • e.g., lungs, intestines, kidneys

Exchange with environment limits animal bodies


  • Basic Animal Function: uptake nutrients, expel waste and exchange gases
    • occurs across plasma membrane of all cells


  • Many animals (like humans) have more complex internal bodies
    • reduces total # of cells on outer surface
    • ‘think’ whale versus flatworm


  • Internal organs for exchange evolve…
    • highly branched or folded
    • digestion, respiration and circulation
    • fluids connect structures to other cells

What are the advantages of a complex body plan?


  • External skeleton?


  • Sensory organs (eyes, ears, etc.)?


  • Internal digestion organs?


  • Specialized filtration systems?



  • How do internal systems allow life on land?

Hierarchy of animal body plans


  • Cells with similar function grouped into tissues


  • Different tissues organized into functional units: Organs


  • Groups of organs can work together: Organ systems


  • There are a limited set of tissues in animals
  1. epithelial:
  2. connective:
  3. muscle:
  4. nervous: